BMP转JPG（法一）使用jpeglib库实现bmp转jpg (转)

来自：http://blog.csdn.net/chenyujing1234/article/details/7730478

一、vc编译jpeglib库

1、下载源代码

下载地址：http://www.ijg.org/。注意：一定要下载win32 版本

2、编译源代码.

A、解压源代码，修改源代码中jconfig.vc为jconfig.h；

B、添加环境变量PATH，C:/Program Files/Microsoft Visual Studio/VC98/Bin ；

C、修改makefile.vc，将 Pull in standard variable definitions下面的一行换为：!include <C:/Program Files/Microsoft Visual Studio/VC98/Include/win32.mak> ；

D、进入命令提示环境下，输入：vcvars32 回车，这是一个用来设置VC路径环境的批处理；

E、编译生成库文件 命令：nmake /f makefile.vc nodebug=1；

这样就OK了

3、jpeglib库VC下使用

对于库的使用只需要有相应的.lib文件和头文件就可以了。Vc中要添加libjpeg.lib库的连接

将这几个文件拷贝到你的项目中：libjpeg.lib，jconfig.h，jmorecfg.h，jpeglib.h，在你需要进行压缩的文件中加入

extern "C" {

#include "jpeglib.h"

#include "jmorecfg.h"

#include "jconfig.h"

}

参考：

http://blog.csdn.net/xingyu19871124/archive/2009/06/30/4310800.aspx

小知识：bmp文件的前54个字节是头，后面才是像素值。

二、使用jpeg库压缩

在源代码的文件夹下面有一个example.c的文件和libjpeg.txt，很有参考价值。

1、基本思路

首先调用截屏程序，将屏幕的位图信息存放在一个buffer里面，然后调用jpg压缩函数，在当前的目录下生成一个ok.jpg的文件。

效果图：

2、出现的问题：

A、运行是总是报错：

我参考源代码的例子，也用JSAMPLE * image_buffer;来指向位图的像素的首地址，编译可以通过但是运行时就会报错，后来我用BYTE *image_buffer;来定义就可以正常运行了。

B、生成的jpg图像失真：以下是对比图片



由于window的位图的像素格式是：BGRA，4个字节，jpeglib库使用的是RGB，3个字节的格式，所以需要将源像素去掉其透明字节，同时改变RGB的顺序。代码如下：

[cpp]
view plaincopyprint?

//RGB顺序调整

for (int i=0, int j=0; j < 1440*900*4; i+=3, j+=4)
{
*(image_buffer+i)=*(image_buffer+j+2);
*(image_buffer+i+1)=*(image_buffer+j+1);
*(image_buffer+i+2)=*(image_buffer+j);
}

//RGB顺序调整

for (int i=0, int j=0; j < 1440*900*4; i+=3, j+=4)
{
*(image_buffer+i)=*(image_buffer+j+2);
*(image_buffer+i+1)=*(image_buffer+j+1);
*(image_buffer+i+2)=*(image_buffer+j);
}

C、生成的jpg文件图像是倒的：



原因没有找到，后来修改了压缩函数的代码，生成了正确的jpg文件

[cpp]
view plaincopyprint?

while (cinfo.next_scanline < cinfo.image_height)
{
//这里我做过修改，由于jpg文件的图像是倒的，所以改了一下读的顺序

//这是原代码：
//row_pointer[0] = & bits[cinfo.next_scanline * row_stride];

row_pointer[0] = & bits[(cinfo.image_height - cinfo.next_scanline - 1) * row_stride];
(void) jpeg_write_scanlines(&cinfo, row_pointer, 1);
}

while (cinfo.next_scanline < cinfo.image_height)
{
//这里我做过修改，由于jpg文件的图像是倒的，所以改了一下读的顺序
//这是原代码：
//row_pointer[0] = & bits[cinfo.next_scanline * row_stride];
row_pointer[0] = & bits[(cinfo.image_height - cinfo.next_scanline - 1) * row_stride];
(void) jpeg_write_scanlines(&cinfo, row_pointer, 1);
}

3、测试结果：

我编写了测试代码，连续截屏并生成jpg文件100次，大约花费7秒左右，也就是说1秒可以截屏13次左右。同时生成的jpg文件有100多K的样子。

三、代码

[cpp]
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#define JPEG_QUALITY 50 //它的大小决定jpg的质量好坏

//#include <atlbase.h>
#include <afxwin.h>

extern "C" {
#include "jpeglib.h"
#include "jmorecfg.h"
#include "jconfig.h"
}
int savejpeg(char *filename, unsigned char *bits, int width, int height, int depth);
void CapScreen(char filename[]);

BYTE *image_buffer; //指向位图buffer的全局指针，window下像素格式: BGRA(4个字节)

int main(int argc, char* argv[])
{
image_buffer = (BYTE *)malloc(1440 * 900 * 4);
for(int i = 0; i < 100; i++)
{
CapScreen("palm.bmp");
//RGB顺序调整
for (int i=0, j=0; j < 1440*900*4; i+=3, j+=4)
{
*(image_buffer+i)=*(image_buffer+j+2);
*(image_buffer+i+1)=*(image_buffer+j+1);
*(image_buffer+i+2)=*(image_buffer+j);
}
savejpeg("ok.jpg", image_buffer, 1440, 900, 3);
}
delete [] image_buffer;
return 0;
}

//===================================================================================

//function: jpeg压缩
//input: 1:生成的文件名,2:bmp的指针,3:位图宽度,4:位图高度,5:颜色深度

//return: int
//description: bmp的像素格式为(RGB)
//===================================================================================

int savejpeg(char *filename, unsigned char *bits, int width, int height, int depth)
{
struct jpeg_compress_struct cinfo;
struct jpeg_error_mgr jerr;
FILE * outfile; //target file

JSAMPROW row_pointer[1]; //pointer to JSAMPLE row[s]

int row_stride; //physical row width in image buffer

cinfo.err = jpeg_std_error(&jerr);
jpeg_create_compress(&cinfo);

if ((outfile = fopen(filename, "wb")) == NULL)
{
fprintf(stderr, "can't open %s/n", filename);
return -1;
}
jpeg_stdio_dest(&cinfo, outfile);
cinfo.image_width = width; //image width and height, in pixels

cinfo.image_height = height;
cinfo.input_components = 3; //# of color components per pixel

cinfo.in_color_space = JCS_RGB; //colorspace of input image

jpeg_set_defaults(&cinfo);
jpeg_set_quality(&cinfo, JPEG_QUALITY, TRUE );//limit to baseline-JPEG values

jpeg_start_compress(&cinfo, TRUE);

row_stride = width * depth; // JSAMPLEs per row in image_buffer

while (cinfo.next_scanline < cinfo.image_height)
{
//这里我做过修改，由于jpg文件的图像是倒的，所以改了一下读的顺序
//这是原代码：
//row_pointer[0] = & bits[cinfo.next_scanline * row_stride];

row_pointer[0] = & bits[(cinfo.image_height - cinfo.next_scanline - 1) * row_stride];
(void) jpeg_write_scanlines(&cinfo, row_pointer, 1);
}
jpeg_finish_compress(&cinfo);
fclose(outfile);
jpeg_destroy_compress(&cinfo);
return 0;
}

void CapScreen(char filename[])
{
CDC *pDC;
pDC = CDC::FromHandle(GetDC(GetDesktopWindow()));
if(pDC == NULL) return;
int BitPerPixel = pDC->GetDeviceCaps(BITSPIXEL);
int Width = pDC->GetDeviceCaps(HORZRES);
int Height = pDC->GetDeviceCaps(VERTRES);

CDC memDC;
if(memDC.CreateCompatibleDC(pDC) == 0) return;
CBitmap memBitmap, *oldmemBitmap;
if(memBitmap.CreateCompatibleBitmap(pDC, Width, Height) == NULL) return;
oldmemBitmap = memDC.SelectObject(&memBitmap);
if(oldmemBitmap == NULL) return;
if(memDC.BitBlt(0, 0, Width, Height, pDC, 0, 0, SRCCOPY) == 0) return;

BITMAP bmp;

memBitmap.GetBitmap(&bmp);

//fp = fopen(filename, "w+b");

BITMAPINFOHEADER bih = {0};
bih.biBitCount = bmp.bmBitsPixel;
bih.biCompression = BI_RGB;
bih.biHeight = bmp.bmHeight;
bih.biPlanes = 1;
bih.biSize = sizeof(BITMAPINFOHEADER);
bih.biSizeImage = bmp.bmWidthBytes * bmp.bmHeight;
bih.biWidth = bmp.bmWidth;

BITMAPFILEHEADER bfh = {0};

bfh.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);
bfh.bfSize = bfh.bfOffBits + bmp.bmWidthBytes * bmp.bmHeight;
bfh.bfType = (WORD)0x4d42;

//fwrite(&bfh, 1, sizeof(BITMAPFILEHEADER), fp);

//fwrite(&bih, 1, sizeof(BITMAPINFOHEADER), fp);

image_buffer = new BYTE[bmp.bmWidthBytes * bmp.bmHeight];

GetDIBits(memDC.m_hDC,
(HBITMAP) memBitmap.m_hObject,
0,
Height,
image_buffer,
(LPBITMAPINFO) &bih,
DIB_RGB_COLORS);
memDC.SelectObject(oldmemBitmap);
//fwrite(p, 1, 1280 * 800 * 4, fp);
//fclose(fp);
}

#define JPEG_QUALITY 50     //它的大小决定jpg的质量好坏
//#include <atlbase.h>
#include <afxwin.h>

extern "C" {
#include "jpeglib.h"
#include "jmorecfg.h"
#include "jconfig.h"
}
int savejpeg(char *filename, unsigned char *bits, int width, int height, int depth);
void CapScreen(char filename[]);

BYTE *image_buffer; //指向位图buffer的全局指针，window下像素格式: BGRA(4个字节)

int main(int argc, char* argv[])
{
image_buffer = (BYTE *)malloc(1440 * 900 * 4);
for(int i = 0; i < 100; i++)
{
CapScreen("palm.bmp");
//RGB顺序调整
for (int i=0, j=0; j < 1440*900*4; i+=3, j+=4)
{
*(image_buffer+i)=*(image_buffer+j+2);
*(image_buffer+i+1)=*(image_buffer+j+1);
*(image_buffer+i+2)=*(image_buffer+j);
}
savejpeg("ok.jpg", image_buffer, 1440, 900, 3);
}
delete [] image_buffer;
return 0;
}

//===================================================================================
//function:       jpeg压缩
//input:          1:生成的文件名,2:bmp的指针,3:位图宽度,4:位图高度,5:颜色深度
//return:         int
//description:    bmp的像素格式为(RGB)
//===================================================================================
int savejpeg(char *filename, unsigned char *bits, int width, int height, int depth)
{
struct jpeg_compress_struct cinfo;
struct jpeg_error_mgr jerr;
FILE * outfile;                 //target file
JSAMPROW row_pointer[1];        //pointer to JSAMPLE row[s]
int     row_stride;             //physical row width in image buffer
cinfo.err = jpeg_std_error(&jerr);
jpeg_create_compress(&cinfo);

if ((outfile = fopen(filename, "wb")) == NULL)
{
fprintf(stderr, "can't open %s/n", filename);
return -1;
}
jpeg_stdio_dest(&cinfo, outfile);
cinfo.image_width = width;      //image width and height, in pixels
cinfo.image_height = height;
cinfo.input_components = 3;         //# of color components per pixel
cinfo.in_color_space = JCS_RGB;         //colorspace of input image
jpeg_set_defaults(&cinfo);
jpeg_set_quality(&cinfo, JPEG_QUALITY, TRUE );//limit to baseline-JPEG values
jpeg_start_compress(&cinfo, TRUE);

row_stride = width * depth; // JSAMPLEs per row in image_buffer
while (cinfo.next_scanline < cinfo.image_height)
{
//这里我做过修改，由于jpg文件的图像是倒的，所以改了一下读的顺序
//这是原代码：
//row_pointer[0] = & bits[cinfo.next_scanline * row_stride];
row_pointer[0] = & bits[(cinfo.image_height - cinfo.next_scanline - 1) * row_stride];
(void) jpeg_write_scanlines(&cinfo, row_pointer, 1);
}
jpeg_finish_compress(&cinfo);
fclose(outfile);
jpeg_destroy_compress(&cinfo);
return 0;
}

void CapScreen(char filename[])
{
CDC *pDC;
pDC = CDC::FromHandle(GetDC(GetDesktopWindow()));
if(pDC == NULL) return;
int BitPerPixel = pDC->GetDeviceCaps(BITSPIXEL);
int Width = pDC->GetDeviceCaps(HORZRES);
int Height = pDC->GetDeviceCaps(VERTRES);

CDC memDC;
if(memDC.CreateCompatibleDC(pDC) == 0) return;
CBitmap memBitmap, *oldmemBitmap;
if(memBitmap.CreateCompatibleBitmap(pDC, Width, Height) == NULL) return;
oldmemBitmap = memDC.SelectObject(&memBitmap);
if(oldmemBitmap == NULL) return;
if(memDC.BitBlt(0, 0, Width, Height, pDC, 0, 0, SRCCOPY) == 0) return;

BITMAP bmp;

memBitmap.GetBitmap(&bmp);

//fp = fopen(filename, "w+b");

BITMAPINFOHEADER bih = {0};
bih.biBitCount = bmp.bmBitsPixel;
bih.biCompression = BI_RGB;
bih.biHeight = bmp.bmHeight;
bih.biPlanes = 1;
bih.biSize = sizeof(BITMAPINFOHEADER);
bih.biSizeImage = bmp.bmWidthBytes * bmp.bmHeight;
bih.biWidth = bmp.bmWidth;

BITMAPFILEHEADER bfh = {0};

bfh.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);
bfh.bfSize = bfh.bfOffBits + bmp.bmWidthBytes * bmp.bmHeight;
bfh.bfType = (WORD)0x4d42;

//fwrite(&bfh, 1, sizeof(BITMAPFILEHEADER), fp);

//fwrite(&bih, 1, sizeof(BITMAPINFOHEADER), fp);

image_buffer = new BYTE[bmp.bmWidthBytes * bmp.bmHeight];

GetDIBits(memDC.m_hDC,
(HBITMAP) memBitmap.m_hObject,
0,
Height,
image_buffer,
(LPBITMAPINFO) &bih,
DIB_RGB_COLORS);
memDC.SelectObject(oldmemBitmap);
//fwrite(p, 1, 1280 * 800 * 4, fp);
//fclose(fp);
}